Testing the accuracy of the ionospheric Faraday rotation corrections through LOFAR observations of bright northern pulsars

Porayko, N. K.; Noutsos, A.; Tiburzi, C.; Verbiest, J. P. W.; Horneffer, A.; Künsemöller, Jörn; Osłowski, S.; Krämer, M.; Schnitzeler, Dominic; Anderson, J. M.; Brüggen, M.; Grießmeier, J.-M.; Hoeft, M.; Schwarz, Dominik J.; Serylak, M.; Wucknitz, O.

doi:10.1093/mnras/sty3324

Cited by 28 publications

(22 citation statements)

References 64 publications

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“…While a single LOFAR station as used here only has a limited effective area or telescope gain, it allows for very flexible scheduling, especially for long observations. The capability of this setup for pulsar science has already been demonstrated (Rajwade et al 2016;Mereghetti et al 2016;Bondonneau et al 2017Bondonneau et al , 2020Michilli et al 2018;Hermsen et al 2018;Donner et al 2019;Porayko et al 2019;Tiburzi et al 2019).…”

Section: Observationsmentioning

confidence: 92%

Follow-up of 27 radio-quiet gamma-ray pulsars at 110–190 MHz using the international LOFAR station FR606

Grießmeier

Smith

Theureau

et al. 2021

A&A

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Context. The Fermi Large Area Telescope has detected over 260 gamma-ray pulsars. About one quarter of these are labeled as radio-quiet, that is they either have radio flux densities < 30 μJy at 1400 MHz, or they are not detected at all in the radio domain. In the population of nonrecycled gamma-ray pulsars, the fraction of radio-quiet pulsars is higher, about one half. Aims. Most radio observations of gamma-ray pulsars have been performed at frequencies between 300 MHz and 2 GHz. However, pulsar radio fluxes increase rapidly with decreasing frequency, and their radio beams often broaden at low frequencies. As a consequence, some of these pulsars might be detectable at low radio frequencies even when no radio flux is detected above 300 MHz. Our aim is to test this hypothesis with low-frequency radio observations. Methods. We have observed 27 Fermi-discovered gamma-ray pulsars with the international LOw Frequency ARray (LOFAR) station FR606 in single-station mode. We used the LOFAR high band antenna band (110−190 MHz), with an average observing time of 13 h per target. Part of the data had to be discarded due to radio frequency interference. On average, we kept 9 h of observation per target after the removal of affected datasets, resulting in a sensitivity for pulse-averaged flux on the order of 1−10 mJy. Results. We do not detect radio pulsations from any of the 27 sources, and we establish stringent upper limits on their low-frequency radio fluxes. These nondetections are compatible with the upper limits derived from radio observations at other frequencies. We also determine the pulsars’ geometry from the gamma-ray profiles to see for which pulsars the low-frequency radio beam is expected to cross Earth. Conclusions. This set of observations provides the most constraining upper limits on the flux density at 150 MHz for 27 radio-quiet gamma-ray pulsars. In spite of the beam-widening expected at low radio frequencies, most of our nondetections can be explained by an unfavorable viewing geometry; for the remaining observations, especially those of pulsars detected at higher frequencies, the nondetection is compatible with insufficient sensitivity.

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Section: Observationsmentioning

confidence: 92%

Follow-up of 27 radio-quiet gamma-ray pulsars at 110–190 MHz using the international LOFAR station FR606

Grießmeier

Smith

Theureau

et al. 2021

A&A

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“…Additionally, the near-Earth environment can be traced through Faraday rotation probes of coronal mass ejections (CMEs; e.g., [175,176]) and studies of the ionosphere through the resulting distortions in source positions (e.g., [177]) and eventually RMs (e.g., [178,179]).…”

Section: The Interstellar Medium and Star Formationmentioning

confidence: 99%

“…Ionospheric RM is usually approximated as the integral of the product of electron content and ionospheric magnetic fields in a thin shell approximation. Recently, the performance and the accuracy of publicly available global ionospheric maps have been rigorously compared using LOFAR pulsar RM observations [179]. While predictions using different geomagnetic fields mostly agree with each other, the accuracy of ionospheric RMs is dominated by the ionospheric total electron content maps: the JPLG [226] and UQRGmaps [227] are found to be superior.…”

Section: Calibration and Widefield Imagingmentioning

confidence: 99%

Magnetism Science with the Square Kilometre Array

Heald¹,

Mao

Vacca³

et al. 2020

Galaxies

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The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.

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“…The continuing pulsar monitoring campaign observes more than 100 pulsars weekly in the high band (Michilli et al 2018, Shaifullah et al 2018, Porayko et al 2019, Donner et al 2019). The signal is digitised at the station and channelised by a polyphase filterbank into 195 kHz-wide subbands.…”

Section: Observationsmentioning

confidence: 99%

On the usefulness of existing solar wind models for pulsar timing corrections

Tiburzi

Verbiest

Shaifullah

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Dispersive delays due to the Solar wind introduce excess noise in high-precision pulsar timing experiments, and must be removed in order to achieve the accuracy needed to detect, e.g., low-frequency gravitational waves. In current pulsar timing experiments, this delay is usually removed by approximating the electron density distribution in the Solar wind either as spherically symmetric, or with a two-phase model that describes the contributions from both high-and low-speed phases of the Solar wind. However, no dataset has previously been available to test the performance and limitations of these models over extended timescales and with sufficient sensitivity. Here we present the results of such a test with an optimal dataset of observations of pulsar J0034−0534, taken with the German stations of LOFAR. We conclude that the spherical approximation performs systematically better than the two-phase model at almost all angular distances, with a residual root-mean-square (rms) given by the two-phase model being up to 28% larger than the result obtained with the spherical approximation. Nevertheless, the spherical approximation remains insufficiently accurate in modelling the Solar-wind delay (especially within 20 degrees of angular distance from the Sun), as it leaves timing residuals with rms values that reach the equivalent of 0.3 µs at 1400 MHz. This is because a spherical model ignores the large daily variations in electron density observed in the Solar wind. In the short term, broadband observations or simultaneous observations at low frequencies are the most promising way forward to correct for Solar-wind induced delay variations.

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Testing the accuracy of the ionospheric Faraday rotation corrections through LOFAR observations of bright northern pulsars

Cited by 28 publications

References 64 publications

Follow-up of 27 radio-quiet gamma-ray pulsars at 110–190 MHz using the international LOFAR station FR606

Follow-up of 27 radio-quiet gamma-ray pulsars at 110–190 MHz using the international LOFAR station FR606

Magnetism Science with the Square Kilometre Array

On the usefulness of existing solar wind models for pulsar timing corrections

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